I can confirm that the shutter release cable will work even with lock on, for both my Rollei 2.8F TLR and SL66. In fact, I remembered reading online from several places, whenever using a release cable, the lock must be on, for the SL66, at least. Doing otherwise may damage the transport mechanism for the SL66. One example is here (there was a url link here which no longer exists)
The advice may or may not be applicable to the Rollei TLR, but I always follow it even when using my 2.8f nonetheless.